1. Field of the Invention:
This invention relates generally to internal combustion engines. More particularly, the invention relates to an internal combustion engine of the type wherein an engine body itself is rotated to drive an output shaft.
2. Description of the Related Art:
As is well known, most of the conventional internal combustion engines equally incorporate a crank mechanism for converting piston reciprocation into rotation of the output shaft. Such a crank mechanism has been found to result in a non-negligible energy loss.
In view of the above problem, U.S. Pat. No. 5,133,305 of the same applicants discloses an internal combustion engine in which a pair of pistons are made to rotate with a cylindrical engine body as the pistons reciprocate in response to explosive combustion occurring in a combustion chamber between the pistons. The rotation of the engine body is directly transmitted to an output shaft without requiring a crank mechanism.
Specifically, the engine body disclosed in the above U.S. patent is rotatably received in a pair of cam cylinders, and has two pairs of longitudinal guide slots. The respective pistons have guide projections slidably guided by the longitudinal guide slots of the engine body, so that the pistons are rotatable with but slidably reciprocatable relative to the engine body. Each cam cylinder is internally formed with a curved cam groove, whereas each piston carries a pair of piston pins penetrating through the longitudinal guide slots to fit into the cam groove. The cam groove have such a profile that the piston makes one full rotation with the engine body as the piston makes two reciprocations.
Obviously, the above-described engine requires no crank mechanism, and therefore has an advantage of being higher in energy efficiency than the conventional reciprocating engines. Further, the rotation of the engine body causes air within the combustion chamber to rotate, so that the air can be forcibly and uniformly mixed with the fuel to provide an enhanced combustion efficiency.
However, in the above-described engine, explosive combustion takes place only at the upper deadpoint of piston reciprocation, and the pistons must move inertially from the lower deadpoint to the upper deadpoint. Thus, there is a limitation in increasing the engine output per unit cylinder volume.